Method for coating light alloy rims

Abstract

The present invention relates to a method for coating light alloy rims, to coating materials for use in this method, and to the coated light alloy rims obtained in this way. A primer layer, a base coat layer, and a clear coat layer are applied to a machined light alloy rim blank. The primer layer includes a radiation-curable coating material having an acid number of 10 to 120 mg KOH/g. The clear coat layer has a double-bond density of free-radically polymerizable reactive groups per unit mass of coating material of at least 1 mol/kg. The coating materials can be cured by radiation.

The invention claimed is: 
     
       1. A method for coating light alloy rims, the method comprising:
 applying a primer (A) layer directly on a machined light alloy rim blank comprising a cast aluminum alloy, the primer (A) layer comprising at least one radiation-curable coating material having an acid number in accordance with DIN EN ISO 3682 (by potentiometry) of 10 to 120 mg KOH/g; 
 after applying the primer (A) layer, applying a base coat (B) layer; 
 after applying the base coat (B) layer, applying a radiation-curable clear coat (C) layer on an outside surface of the light alloy rim, the clear coat (C) layer having a double-bond density of free-radically polymerizable reactive groups per unit mass of coating material of at least 1 mol/kg; and 
 curing the primer (A) layer, the clear coat (C) layer, and optionally the base coat (B) layer by high-energy radiation selected from the group consisting of light in the wavelength range of 200 nm to 700 nm, an electron beam in the range of 150 keV to 300 keV, and combinations thereof; 
 wherein: 
 the primer (A) layer is fully cured with the high-energy radiation and without being further heated after being applied; and 
 the primer (A) layer, the base coat (B) layer, and the clear coat (C) layer are different from each other. 
 
     
     
       2. The method of  claim 1 , wherein the primer (A) layer comprises at least one radiation-curable coating material comprising
 (A2a) at least one binder selected from the group consisting of aliphatic urethane (meth)acrylates, aromatic urethane (meth)acrylates, and epoxy (meth)acrylates, 
 (A2b) at least one reactive diluent, and 
 (A2c) optionally at least one anticorrosion pigment and/or corrosion inhibitor. 
 
     
     
       3. The method of  claim 1 , wherein the base coat (B) layer comprises at least one water-based, two-component coating material comprising at least one pigment and/or metallic flakes. 
     
     
       4. The method of  claim 3 , wherein the base coat (B) layer coating material has a solids content of between 20% and 80% by weight. 
     
     
       5. The method of  claim 1 , wherein the base coat (B) layer comprises at least one water-based, radiation-curable coating material comprising at least one pigment and/or metallic flakes. 
     
     
       6. The method of  claim 5 , wherein the base coat (B) layer coating material has a solids content of between 20% and 80% by weight. 
     
     
       7. The method of  claim 1 , comprising performing curing by high-energy radiation under inert gas. 
     
     
       8. The method of  claim 1 , further comprising, after applying the base coat (B) layer and before applying the clear coat (C) layer:
 curing the base coat (B) layer, 
 removing the base coat (B) layer on an outer facing side of the light alloy rim down to bare metal of the light alloy rim, such that during application of the clear coat (C) layer, the clear coat (C) layer is applied to the bare metal. 
 
     
     
       9. The method of  claim 1 , wherein the clear coat (C) layer is fully cured with the high-energy radiation and without being further heated after being applied. 
     
     
       10. The method of  claim 1 , further comprising:
 after applying the primer (A) layer and before applying the base coat (B) layer, partially curing the primer (A) layer with the high-energy radiation, but not fully curing the primer (A) layer; and 
 after applying the clear coat (C) layer, fully curing the primer (A) layer with the high-energy radiation. 
 
     
     
       11. The method of  claim 1 , further comprising:
 after applying the clear coat (C) layer, fully curing the primer (A) layer with the high-energy radiation, wherein the primer (A) layer is not cured with the high-energy radiation after applying the primer (A) layer and before applying the base coat (B) layer.